1. Field of the Invention
An aspect of the present invention relates to a non-linear data converter, an encoder and a decoder.
2. Description of the Related Art
An encoder or a decoder by a common key encoding system such as a DES (Data Encryption Standard) is mounted on an IC card or the like and widely used. It is very important to protect a secret key from an illegal access.
For instance, as disclosed in JP-A-2000-66585 showing a counter measure to an illegal access such as a DPA (Differential Power Analysis) for estimating a secret key from a consumed electric power during the operation of an encoder or a decoder, a method is reported that a predetermined mask value and a mask value obtained by inverting bits thereof are selected at random for each encoding operation or decoding operation to perform a mask process.
However, in JP-A-2000-66585, a resistance to a high-order DPA for estimating the secret key from a consumed electric power at a plurality of timings is not considered.